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.Dd October 26, 2011
.Dt GETGRENT 3
.Os
.Sh NAME
.Nm getgrent ,
.\".Nm getgrent_r ,
.Nm getgrnam ,
.Nm getgrnam_r ,
.Nm getgrgid ,
.Nm getgrgid_r ,
.Nm getgruuid ,
.Nm getgruuid_r ,
.Nm setgroupent ,
.Nm setgrent ,
.Nm endgrent
.Nd group database operations
.Sh LIBRARY
Standard system libraries.
.Sh SYNOPSIS
.In grp.h
.In uuid/uuid.h
.Ft struct group *
.Fn getgrent void
.\".Ft int
.\".Fn getgrent_r "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft struct group *
.Fn getgrnam "const char *name"
.Ft int
.Fn getgrnam_r "const char *name" "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft struct group *
.Fn getgrgid "gid_t gid"
.Ft int
.Fn getgrgid_r "gid_t gid" "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft int
.Fn getgruuid "uuid_t uuid"
.Ft int
.Fn getgruuid_r "uuid_t uuid" "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft int
.Fn setgroupent "int stayopen"
.Ft void
.Fn setgrent void
.Ft void
.Fn endgrent void
.Sh DESCRIPTION
.\"These functions operate on the group database file
These functions obtain information from
.Xr opendirectoryd 8 ,
including records in
.Pa /etc/group
which is described
in
.Xr group 5 .
Each line of the database is defined by the structure
.Vt group
found in the include
file
.In grp.h :
.Bd -literal -offset indent
struct group {
	char	*gr_name;	/* group name */
	char	*gr_passwd;	/* group password */
	gid_t	gr_gid;		/* group id */
	char	**gr_mem;	/* group members */
};
.Ed
.Pp
The functions
.Fn getgrnam ,
.Fn getgrgid ,
and
.Fn getgruuid
search the group database for the given group name pointed to by
.Fa name ,
the group id given by
.Fa gid ,
or the UUID given by
.Fa uuid 
respectively, returning the first one encountered.
Identical group
names, group gids, or uuids may result in undefined behavior.
.Pp
Note that the groups file
.Pa /etc/group
does not contain group UUIDs.
The UUID for a group may be found using
.Fn mbr_gid_to_uuid .
.Pp
On OS X, these routines are thread-safe and return a pointer to a
thread-specific data structure.  The contents of this data
structure are automatically released by subsequent calls to
any of these routines on the same thread, or when the thread exits.
These routines are therefore unsuitable for use in libraries or frameworks,
from where they may overwrite the per-thread data that the calling
application expects to find as a result of its own calls to these
routines. Library and framework code should use the alternative reentrant 
variants detailed below.
.Pp
The
.Fn getgrent
function
searches all available directory services on it's first invocation.
It caches the returned entries in a list
and returns group entries one at a time.
.Pp
.Em NOTE
that 
.Fn getgrent
may cause a very lengthy search for group records by
.Nm opendirectoryd
and may result in a large number of group records being cached
by the calling process.
Use of this function is not advised.
.Pp
The functions
.Fn getgrnam_r , 
.Fn getgrgid_r ,
and
.Fn getgruuid_r
are alternative versions of
.Fn getgrnam ,
.Fn getgrgid ,
and
.Fn getgruuid
respectively.
The caller must provide storage for the results of the search in
the
.Fa grp ,
.Fa buffer ,
.Fa bufsize ,
and
.Fa result
arguments.
When these functions are successful, the
.Fa grp
argument will be filled-in, and a pointer to that argument will be
stored in
.Fa result .
If an entry is not found or an error occurs,
.Fa result
will be set to
.Dv NULL .
.Pp
These functions will open the group file for reading, if necessary.
.Pp
The
.Fn setgroupent
function causes
.Fn getgrent
to ``rewind'' to the beginning of the list of entries cached by a previous
.Fn getgrent
call.
The cache is not cleared.
The
.Fa stayopen
parameter value is unused on OS X.
.Pp
The
.Fn setgrent
and
.Fn endgrent
functions clear the cached results from a previous
.Fn getgrent
call.
.Sh RETURN VALUES
The functions
.Fn getgrent ,
.Fn getgrnam ,
and
.Fn getgrgid ,
return a pointer to a group structure on success or
.Dv NULL
if the entry is not found or if an error occurs.
If an error does occur,
.Va errno
will be set.
Note that programs must explicitly set
.Va errno
to zero before calling any of these functions if they need to
distinguish between a non-existent entry and an error.
The functions
.Fn getgrnam_r ,
.Fn getgrgid_r ,
and
.Fn getgruuid_r
return 0 if no error occurred, or an error number to indicate failure.
It is not an error if a matching entry is not found.
(Thus, if
.Fa result
is set to
.Dv NULL
and the return value is 0, no matching entry exists.)
.Pp
.Fn setgroupent
returns the value 1 if successful, otherwise the value
0 is returned.
The functions
.Fn setgrent ,
.Fn endgrent ,
and
.Fn setgrfile
have no return value.
.Sh FILES
.Bl -tag -width /etc/group -compact
.It Pa /etc/group
group database file
.El
.Sh COMPATIBILITY
The historic function
.Fn setgrfile ,
which allowed the specification of alternate group databases, has
been deprecated and is no longer available.
.Sh SEE ALSO
.Xr getpwent 3 ,
.Xr group 5 ,
.Xr mbr_gid_to_uuid 3, 
.Xr opendirectory 8 ,
.Xr yp 8
.Sh STANDARDS
The
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrnam_r ,
.Fn getgrgid ,
.Fn getgrgid_r
and
.Fn endgrent
functions conform to
.St -p1003.1-96 .
The
.Fn setgrent
function differs from that standard in that its return type is
.Vt int
rather than
.Vt void .
.Sh HISTORY
The functions
.Fn endgrent ,
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrgid ,
and
.Fn setgrent
appeared in
.At v7 .
The functions
.Fn setgrfile
and
.Fn setgroupent
appeared in
.Bx 4.3 Reno .
The functions
.\".Fn getgrent_r ,
.\".Fn getgrnam_r ,
.Fn getgrnam_r
and
.Fn getgrgid_r
appeared in
.Fx 5.1 .
The functions
.Fn getgruuid
and
.Fn getgruuid_r
appeared in Mac OS X 10.8.
.Sh BUGS
The functions
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrgid ,
.Fn getgruuid ,
.Fn setgroupent
and
.Fn setgrent
leave their results in an internal thread-specific memory and return
a pointer to that object.
Subsequent calls to
the same function
will modify the same object.
